This invention relates to recirculating liquid fuel burners.
It is known to use recirculated hot combustion gases to vaporize liquid fuel, such as oil, for blue-flame, smoke-free, and quiet combustion. It has been said that the percent recirculation should be at least 50%, for maintaining blue-flame combustion, but that the percent recirculation necessary increases with the percent excess air used. American Petroleum Institute Publication 1723-A, January, 1965, pp. 2-4, esp. FIG. 1. "Blue-flame combustion", as the term is used hereinafter, will refer to the "Region of clean, blue-flame, quiet combustion" labeled on FIG. 1 of this API publication, reprinted as FIG. 1 of the U.S. patent application of Alex F. Wormser entitled "Recirculating Burner", filed Aug. 22, 1975, Ser. No. 606,841, and hereby incorporated by reference herein. Reichhelm et al. U.S. Pat. No. 3,705,784 and Reichhelm U.S. Pat. No. 3,361,183 teach introducing liquid oil into the flow of recirculated hot gases, the driving force for recirculation being provided by suction owing to ejector action by incoming air, although the former patent specifies recirculation of only a small portion of the gases. Complete vaporization of the oil is desired to attain blue-flame operation, and effective mixing of recirculated hot gases with the liquid fuel is a desirable method of achieving complete vaporization and avoiding unwanted condensation of liquid fuel on the walls of burner apparatus. Von Linde U.S. Pat. No. 3,174,526 teaches spraying atomized liquid fuel into recirculated hot combustion gases in a prechamber slightly upstream of the sites for mixing with air and burning. Bailey U.S. Pat. No. 3,652,194, in a system in which the fuel is premixed with oxidant air before being mixed with a minor proportion of recirculated hot gases, teaches generating vortices at the combustion area by making the burner leg square in cross section, for improved mixing of hot gases with the fuel-air mixture. Thermal Research & Engineering Corp. of Conshohocken, Pa., offers an internally recirculating burner utilizing tangential entry of inlet air to create a vortex to draw back the hot combustion gases (Bulletin No. 143, pp. 6-7).